Distribution of cells in the normal marginal synovium during the postnatal period

Introduction The marginal transitional zone of the joint includes the marginal cartilage and marginal synovium. These tissues are in constant interaction with each other, but differ in morphology, function and metabolism, representing the innate immunobiological border between the joint capsule and articular cartilage. Cells of the non-inflamed marginal synovium take part in joint tissue development, differentiation, remodeling and repair. In the inflamed synovium, they play a leading role in synovial hyperplasia and cartilage destruction. In present-day literature, there are not enough studies about the morphology of the normal marginal synovium.

Methods Cells distribution in the marginal synovial subintima was studied using hip joints of intact Wistar rats with subsequent extrapolation to humans (Sengupta, 2013). The joints were sampled on the first, seventh, 14th, 30th, 45th, 60th and 90th days; n=6). The formalin-fixed, paraffin-embedded tissue sections were stained using hematoxylin and eosin, alcian blau (MgCl2 0.2 M) analyzed by light microscopy (χ100), morphometry and statistics.

Results The marginal synovium includes cells and components of the extracellular matrix, which are typical for the fibrous connective tissue. Among the cells, we distinguished fibroblasts, fibrocytes, mast cells, macrophages and lymphocytes. The maximum number of young fibroblasts was observed in newborns; it subsequently decreased, reaching by the 90th day (approximately 18-19 human years) a figure almost 3.5 times lower than that of newborns. The maximum quantity of mature fibroblasts was observed also in newborns; it decreased by the 30-60th days (approximately 9-16 human years) almost twofold with a slight increase on the 90th day. The number of fibroblasts in newborns was 16.52±2.1; it decreased till the seventh day (early neonatal period of human life) with an increase till the 30th day and subsequent secondary decrease. The quantity of mast cells increased till the 14th day (early infancy) and then decreased. The maximum number of macrophages was in newborns. Subsequently, it gradually decreased. On the 90th day, their quantity was almost one and a half times less than that in newborns. The maximum number of lymphocytes was on the seventh day; it decreased till the 45th day (approximately 14 human years) with a subsequent increase on the 60th day and a secondary decrease on the 90th day.

Tab. 1  marginal synovium.

Discussion The cellular composition of the marginal synovium is generally similar to the synovial subintima of the joint capsule, which is consistent with Allard et al. (1990). However, we cannot agree with statements about the absence of macrophages and mast cells (Thompson & Stockwell 1983) as well as lymphocytes (Allard et al. 1990) in the marginal synovium. Changes in the distribution of cells during morphogenesis of the marginal synovium emphasize complex cell-cell and cell-matrix relationships in it. Non-altered cellular composition of the marginal synovium provides anatomophysiological integrity of the marginal transitional zone and joint as a whole. In the marginal synovium, fibroblasts and macrophages showed a downward trend in their distribution. In turn, the distribution of fibrocytes and mast cells had an undulatory pattern. The above data deepen our knowledge about the morphogenesis of the normal marginal synovium and will assist in understanding the pathology regarding normal anatomy.

Keywords joint, marginal synovium, Wistar rats

Korrespondenzadresse Andrii Fedotchenko, Asklepios Clinik Altona, Paul-Ehrlich-Straße 1, 22763 Hamburg, Germany, E-Mail: [e-mail]

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Artikel online veröffentlicht:
16. Juni 2023